Introduction to the functions of the three major components of a belt conveyor

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Belt conveyors feature large handling capacity, simple structure, easy maintenance, low cost, and high versatility, and are widely used in various sectors such as metallurgy, coal, transportation, hydropower, chemicals, building materials, light industry, grain processing, ports, and shipbuilding. A belt conveyor is mainly composed of a frame, conveyor belt, idler rollers, drive rollers, tensioning device, transmission device, etc. The three main components of a belt conveyor are what we call the drive unit, the tensioning unit, and the steering unit. Let’s take a look at the specific functions of these three devices. Drive mechanism: The drive mechanism of a belt conveyor consists of an electric motor, coupling or hydraulic coupling, reducer, drive pulley, etc. Belt conveyors with inclined sections should also be equipped with brakes or check valves as required. The function of the drive mechanism is to transmit force to the conveyor belt through friction via the drive drum, thereby moving the belt and transporting goods. Most belt conveyors use a single drum drive, but as the volume and distance of transportation increase, there is a corresponding need for greater traction force to be transmitted by the drive drum; as a result, dual-drum and multi-drum drives have been developed. Each drive drum can be equipped with one or two drive units, and the end of the drive drum shaft is connected to the drive units via couplings. Drive motors generally use Y-series squirrel-cage motors, which offer the advantages of small size, low cost, reliable operation, and ease of automatic control. When the power is low (≤37kW), it can be driven directly via an elastic coupling ； When the power is high (45–315 kW), a hydraulic coupler can be used to ensure a smooth start-up. At high power levels (220–800 kW), wound-rotor motors can be used; they are easy to control, enabling smooth startup of long-distance belt conveyors and addressing the power balance issue in multi-drum drives. In modern large-scale belt conveyors, in addition to cylindrical gear drives, bevel gear reducers are also often used in order to reduce the lateral dimensions of the conveyor’s drive unit. For mobile belt conveyors, in order to reduce their own weight, drive systems often use belts, chains, or single-stage open gear drives. In addition, a cycloidal pinwheel reducer or an electric drum can also be used. An electric drum integrates the motor and reduction gear inside the drive drum, resulting in a compact structure, low weight, easy installation, and safe operation; it is suitable for humid and corrosive working environments. Its disadvantage is that the motor has poor heat dissipation conditions and is inconvenient to maintain. The drive drum transmits traction through the friction between its surface and the conveyor belt. Drive rollers are available in smooth and rubber-coated versions; the rubber-coated variants include flat rubber surfaces, V-patterned rubber surfaces (suitable for one-way operation), and diamond-patterned rubber surfaces (suitable for two-way operation). The use of rubber surfaces, especially those with patterns, can increase the friction coefficient; patterned rubber surfaces also play a role in preventing the conveyor belt from drifting. Use smooth rollers in situations with low power and low environmental humidity ； Rubber-coated rollers should be used when the environment is humid, the power is high, and slipping is likely to occur. When the conveyor belt passes around the drum, bending causes fatigue damage. Therefore, the diameter of the drive drum cannot be too small. The diameter options for the drive drum are 500, 630, 800, 1000 mm, etc., and can be selected according to the belt width. Tensioning device: The function of the tensioning device is to maintain the necessary initial tension in the conveyor belt, thereby preventing slippage on the drive drum and ensuring that the sag of the conveyor belt between the idler rollers remains within the specified range. Tensioning devices mainly include screw-type, trolley-weight type, and vertical weight type. 1) The screw-type tensioning device uses manual rotation of a screw to adjust the tension of the conveyor belt. Its structure is simple and compact, but it is difficult to control the tension level, and the tension cannot remain constant during operation. It is generally used in conveyors with a length of less than 100m and low power, and the stroke length can be selected at 1%-1.5% of the machine length. 2) The small-car weight-hammer type tensioning device has large dimensions, occupies a lot of space, and has a heavy weight; it is suitable for conveyors with large lengths and high power, especially on inclined conveyors. 3) The vertical weight-type tensioning device can make use of the space below the conveyor corridor and be installed at the point where the tension on the lower belt branch is lowest, thereby reducing the mass of the weight. Its disadvantage is that it requires an increase in the number of redirecting drums, leading to more bends in the conveyor belt; moreover, materials can easily fall between the conveyor belt and the drums, damaging the belt. Direction-changing device: Belt conveyors use direction-changing drums or sets of direction-changing idlers to change the movement direction of the conveyor belt. Direction-changing drums can be used to change the direction of the conveyor belt by 180°, 90°, or <45°. A redirecting drum located at the tail end or a vertical weight-type tensioning drum is used to redirect the conveyor belt by 180°; the drum above the vertical weight tensioning device redirects it by 90°, while a redirection of less than 45° is generally used to increase the wrap angle between the conveyor belt and the drive drum. The diameter of the direction-changing drum is available in sizes such as 250, 315, 400, 500, 630, 800, and 1000 mm; it can be selected to match the diameter of the drive drum. When reversing by 180°, its diameter can be one size smaller than that of the drive drum; when reversing by 90° or 45°, it can be appropriately reduced by 1–2 sizes as the reversal angle decreases. The redirecting idler set consists of several support idlers arranged along an arc of the desired radius. It is used in areas where the conveyor belt bends over a large curvature radius, or in sections with trough idlers, to ensure that the conveyor belt maintains its trough-shaped cross-section at the points of redirection. When the conveyor belt passes through the convex arc section, due to the effect of the idler groove angles, the elongation rates on both sides of the conveyor belt are greater than that at the center. To reduce tape stress, the radius of curvature of the convex arc section should be as large as possible, typically with an elongation rate of 0.8% for the fabric core tape.